This invention relates generally to electrical discharge machining and more particularly to handling electrodes used in electrical discharge machining.
Electrical discharge machining (EDM) is a well known process for forming features, such as holes, slots and notches of various shapes and configurations, in an electrically conductive workpiece. Conventional EDM apparatuses typically employ an electrode, having a specific shape, that is advanced toward the workpiece. A suitable power supply is applied to create an electrical potential between the workpiece and electrode for forming a controlled spark which melts and vaporizes the workpiece material to form the desired feature. The cutting pattern of the electrode is usually computer numerically controlled (CNC) whereby servomotors control the relative positions of the electrode and workpiece. During machining, the electrode and workpiece are immersed in a dielectric fluid, which provides insulation against premature spark discharge, cools the machined area, and flushes away the removed material.
There are many EDM operations in which several distinct features are machined into a single workpiece. For example, turbine blades used in gas turbine engines commonly have many cooling holes formed therein. The cooling holes permit an outflow of coolant from internal passages to effectively cool the blade during its high temperature operation. These cooling holes are ordinarily formed by an EDM procedure. To increase the manufacturing output of such parts, it is common to use an EDM electrode having a plurality of prongs or stingers that are sized and shaped to machine a row of cooling holes in a single operation. Such electrodes are known as a comb electrodes.
Given the nature of the EDM process, the electrodes wear down quickly and must be replaced often. Typically, a new electrode is used for each part that is machined. Each time an electrode is replaced, the EDM operator must remove the new electrode from its packing and load it by hand into the electrode holder of the EDM apparatus. This process results in a lot of manual handling of the electrodes. Current packaging procedures by the electrode manufacture also entail much manual handling of the electrodes.
Comb electrodes are very fragile and easily damaged during transportation from the manufacturer and handling by the end user. A badly damaged electrode is unusable and must be discarded, resulting in the loss of the cost of the electrode. Even more troublesome with comb electrodes is that the stingers can become slightly bent during manual handling. The amount of damage can be so minimal that the operator does not realize that the electrode is damaged and proceeds with the EDM operation. However, even an undetectable amount of stinger bend can result in a misaligned or malformed feature that requires the entire part to be scrapped, which can represent a substantial cost.
Current efforts to avoid damaged electrodes are limited to operator awareness training. However, such training efforts do not address the root cause of damaged electrodes, which is the large amount of manual handling of the electrodes. Accordingly, it is desirable to have a means for replacing EDM electrodes that eliminates or greatly reduces the amount of manual handling of the electrodes.
The above-mentioned need is met by the present invention, which provides an electrode holding and dispensing assembly for use with an electrical discharge machining apparatus. The assembly includes a guide rail having a channel formed therein and an electrode dispenser positioned to deliver electrodes to the channel. A slider is slidingly received in the channel for advancing electrodes delivered to the channel from the dispenser to an electrode seating site located in the channel, where the electrode is securely held during machining operations.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.